Outbreak, first reported in a remote rural area, has its first confirmed case in Mbandaka, a city of 1.2 million.

Three new cases of Ebola have been confirmed in the Democratic Republic of the Congo's (DRC) sprawling northwest, taking the number of suspected infections to 43, according to the health minister.

The outbreak, previously reported in a remote rural area of the country, recorded its first confirmed cases in Mbandaka, a city of 1.2 million, as the spread of the haemorrhagic fever raised alarm.

"Three new cases were reported (in Mbandaka) and tested positive for the Ebola virus," Health Minister Oly Ilunga said in the statement.

"In total, 43 cases of haemorrhagic fever have been flagged in the region of which 17 are confirmed, 21 are probable, and five are suspected cases," he said.

In Geneva, the United Nations's World Health Organization (WHO) put the death toll at 25 but said 45 cases have been recorded, 14 of which have been confirmed by lab tests.

WHO: No global emergency

The WHO on Friday said the latest Ebola outbreak did not warrant being labelled an emergency of "international concern", adding that Kinshasa's response along with its own had been "rapid and comprehensive".

The government announced the outbreak of the deadly virus in northwestern Equateur province on May 8.

In the WHO's parlance, "a public health emergency of international concern" is an "extraordinary event" in which a disease may spread across borders and requires a vigorous international response.

Ebola is both lethal and highly contagious, which makes it difficult to contain, especially in urban environments where people are mobile and come into contact with others more often.

It is notorious for its high fatality rate and extreme symptoms, which can include internal and external bleeding.

The current outbreak, the ninth to hit the DRC since Ebola was identified in 1976, involves the same strain of the virus that struck three West African countries in 2013-2015 and sparked an international panic.

It went on to kill more than 11,300 people in the deadliest ever Ebola epidemic.